Our hypothesis is that there are demonstrable phenotypic differences between new and mature a cells that will provide important information about beta cell birth and death. Using laser capture microdissection and Affymetrix GeneChips, gene profiling data was generated comparing the beta cell-enriched cores of new and mature islets from the same rats after partial pancreatectomy (Px) and of islets from sham operated animals. The comparison of mature vs. sham islets reflects changes in environment but that between new vs. mature islets reflect age differences. These data show clear effects of age of beta cells on differential gene expression. The first aim is to develop markers that can be used for determining beta cell maturity from early stages just as the a cell has differentiated from precursor/stem cells to mature functional a cells. Several such markers have already been confirmed by RT-PCR and immunostaining within the regenerating pancreas as well as with neonatal islets, in which all a cells must be new. These markers will then be used in the second aim to determine the distribution of new and mature beta cells in different aged animals, which should answer fundamental questions about a cell life history. In the third aim these markers will be used to separate new and mature a cells to give relatively pure populations for analysis of their function both in vitro and in vivo following transplantation. With gene profiling of these pure populations the genetic "fingerprints" of the different stages of the beta cell through its life history will be determined; these fingerprints will be valuable for assessing the maturity of stem cell-derived insulin producing cells and in our future identification of the precursor/stem cells that give rise to a cells after birth. Another important outcome of this research should be valuable information about such practical questions as what will lead to successful long-term islet transplantation.